In addition, the Eurozone core is convinced, especially Germany, that the financial risks are finally ringfenced and Grexit is manageable.

I think this is key.

While Germany believes that Grexit is manageable, Grexit gets ever more likely, because what reason is there for Germany to compromise?

And it has to be clear eventually to Syriza that it is impossible to satisfy Germany and save the Greek economy.

Hence - Grexit.